Tony Blair is set to deliver a speech in London which makes little attempt to hide his dislike of populism.
Photograph: Stefan Rousseau/PA

A return to the dark politics of the 1930s is no longer far-fetched today because of rampant nationalist populism and the widespread rejection of multilateral alliances, according to Tony Blair.

In a stark speech to the Chatham House thinktank in London, the former British prime minister will say he has never been so worried about the future of the UK.

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Blair will also tell Donald Trump, ahead of the US president’s visit to Europe next month, that he must act to preserve the transatlantic alliance, or else he will weaken the whole of the west in the struggle against rising nations such as China.

Blair is due to say: “We need to know from the current American administration and its president that our alliance matters, that it is regarded, historically and contemporaneously, as a vital American strategic interest.”

“We are losing sight of the values which brought the west together, saw it through the menace of fascism and communism”, he will add.

Blair also urges the Trump administration to counter “with vigour and urgency” the widely held view that it wants the transatlantic alliance to fracture, saying: “The only people that would gain from this are America’s rivals or adversaries.”

Blair, who has defended strong UK-US relations for more than two decades, is clearly concerned that Trump has no feel for the historical depth of his country’s relationship with Europe, and may see the break-up of the EU as something unimportant or even beneficial to the US.

The former Labour PM is expected to assert: “The transatlantic alliance is the bedrock of our values system and way of life. Yet the rightwing relegation of it as secondary to national interest rather than part of it and the kneejerk leftwing reaction against anything American-led, is leaving this alliance in danger of fracture

“We need leaders both sides of the water explaining its importance and seeking ways of strengthening it.”

Blair, who maintains close relations with Jared Kushner, the president’s son-in-law, mainly over the middle east, will not directly accuse the president of populism, but his speech makes little attempt to hide his dislike of this political style.

He is due to say: “Globalisation and its advocates are on the back foot. Populism of left and right meet at a certain point in denunciation of free trade arrangements, migration and international alliances. All are portrayed as contrary to putting individual national interest first.

“Once it is clear the populism isn’t working because, ultimately, it offers only expressions of anger and not effective answers, the populists may double down, alleging that failure is the result of half-heartedness and that only more of the same will work.

“Who knows where the dynamic of that scenario takes us. Then the comparisons with the 1930s no longer seem far-fetched.”

He will also bluntly tell US diplomats not to imagine that either Brexit or a wider break-up of the EU will be in US interests.

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“America needs Europe united and standing with it, not isolated as individual nations, able to be picked off one by one by the then emerged new powers”.

He will also weigh in on the state of the Brexit talks: “We cannot go on like this. I have never been more worried about the future of our country than now, with competing emotions of anxiety and rage.

“We have a government whose every move is a calculation not about the interests of the nation, but the internal balance of advantage between the factions of the Conservative party, with the prime minister more a hostage than a leader.

“Meanwhile the leader of the Labour party neglects to lead the fight here at home over an issue which literally determines the future of Britain and where he could play a decisive role.”

Blair will call on MPs to assert themselves, adding: “the UK needs to plan now for the possibility we need to extend the March 2019 deadline for the end of the negotiations”.